WASHINGTON Lockheed Martin Corp (LMT.N) was awarded an interim payment of $5.6 billion to help finance the construction of the 11th batch of 141 F-35 jets for the U.S. military and its allies, the U.S. Defense Department said on Friday.

The Pentagon expects to spend $391 billion to develop the plane and buy 2,457 jets, making the F-35 its single most expensive weapons program.

The agreement announced on Friday allows Lockheed to continue production of the F-35 jets while it finalizes the terms of the 11th contract with the Pentagon.